The best WB questions have some or all of these attributes
There isn't one single qualifier or disqualifier for a good, on-topic WB question. It's a constellation of factors. This is why I believe it's been so hard to figure out what is on-topic and what isn't. As I've thought about this problem, I keep running into criteria where I think "Yes, good WB questions have that attribute...yeah, but..."
Combinatorial - Combine systems or elements of systems into new systems or new properties of those systems.
Speculative - The question must include some kind of speculation about things that we don't know about how the system works.
About a System (very broad definition of a system) - The operation of single elements, much like the actions of a single person, don't belong here.
Novel - Please make it new.
Abstract - The nitty gritty details of the answer don't matter, or they can be handwaved.
Not advocating doing dangerous things - Knowing how to do a dangerous/evil thing is different than doing it or advocating that it be done. We have tons of genocide questions on WB but no one advocates that genocide be done. If we have reasonable cause to believe that someone would take dangerous actions based on what we provide, that should be off-topic.
Not homework
Not trivial - Google can't give you the answer to this question.
Always with the Exceptions
Except for the trivial and the homework questions, anyone of us can find fantastic WB questions that offer magnificent exceptions. For example, every single hard-science question cares a lot about the details and often in great specificity. But, note that these hard-science questions are often combinatorial, novel, and about a system. It is all the other attributes that make them good WB questions instead of off-topic.
The relationship between all these criteria are fuzzy. Some are weighted heavier than others. Some are necessary but insufficient (I'm not sure any of them are necessary and sufficient to be a good WB question.) However, the more of these criteria a question has, the stronger its position as a good, on-topic WB question.
What do we want WB to be?
We shouldn't be someone's homework service. I will not be someone's homework service. I want us to be the place that people come for fantastic answers to questions that require novel reasoning about known systems. I want us to be the place where people come to get help with imaginary worlds. Being a repository for useful information about the real world is tertiary to helping people reason about their imaginary worlds. If answering questions about how the real world works and this function impares people's ability to propose and reason about their worlds, then I would vote that real world questions are off-topic.
We aren't an encyclopedia and I don't want to become one.
I don't want us to become the dumping ground of bad questions for all of Stack Exchange either.